A novel impinging stream-rotating packed bed was used to prepare Fe3O4 nanoparticles with aqueous solutions of FeCl3/FeCl2 and NaOH as raw materials. The effects of high gravity factor, liquid flow rate and reactant concentrations on the particle size of Fe3O4 were examined. Moreover, the adsorption property of Fe3O4 nanoparticles to Pb(II) and Cd(II) was evaluated. The results showed that higher high gravity factor, larger liquid flow rate and higher concentration of reactants were associated with smaller size of Fe3O4 nanoparticles. Fe3O4 nanoparticles were quasi-spherical with the average diameter of about 10 nm and showed superparamagnetic behavior with the saturation magnetization of 60.5 emu/g under the optimal operation conditions, which were high gravity factor of 65.32, liquid flow rate of 60 L/h and FeCl3×6H2O concentration of 0.321 mol/L. The adsorption of Fe3O4 nanoparticles to Pb(II) and Cd(II) well fitted to the Langmuir isothermal model, and their maximum adsorption capacities calculated were 30.47 and 13.04 mg/g for at pH value 6.0, respectively.